Process of stabilizing a migration image comprising selenium particles

ABSTRACT

An image comprising migration material residing on a metallic conductive substrate and formed in accordance with the migration imaging process is stabilized and fixed onto the substrate by heating the substrate and the migration material to produce a chemical reaction therebetween resulting in a permanent stable image having high density and resolution.

United States Patent Levy et al.

[151 3,653,885 51 Apr. 4, 1972 [54] PROCESS OF STABILIZING A MIGRATIONIMAGE COMPRISING SELENIUM PARTICLES [72] Inventors: Mortimer Levy,Rochester; Peter P. Au-

gostini, Webster, both of N .Y.

[73] Assignee: Xerox Corporation, Rochester, NY.

[22] Filed: Apr. 20, 1970 [21] Appl. No.: 29,932

Related US. Application Data [63] Continuation-impart of Ser. No.590,959, Oct. 31,

1966, abandoned.

2,962,376 11/1960 Schaffe rt ..96/1.5 3,083,117 3/1963 Schmiedel et al..1 17/1 7.5 3,138,458 6/1964 Kimble et al ..96/1 3,383,209 5/1968Cassiers et al. .96/1.3 3 ,440,045 4/1969 Lind ....96/1 3,440,046 4/1969Droege et al. ..96/27 3,520,681 7/1970 Goffe ..96/1

FOREIGN PATENTS OR APPLICATIONS 1,035,892 7/ 1966 Great Britain ..96/1.5

Primary Examiner-Charles E. Van Horn Attorney-James J. Ralabate, DavidC. Petre and Raymond C. Loyer [57] ABSTRACT An image comprisingmigration material residing on a metallic conductive substrate andformed in accordance with the migration imaging process is stabilizedand fixed onto the substrate by heating the substrate and the migrationmaterial to produce a chemical reaction therebetween resulting in apermanent stable image having high density and resolution.

12 Claims, 8 Drawing Figures Patented April 4, 1972- 3,653,885

F/ 6.-IA FIG. 1B. Fla/c;

INVENTORS MORTIMER LEVY BY PETER P. AUGOSTINI ATTORNEY PROCESS OFSTABILIZING A MIGRATION IMAGE COMPRISING SELENIUM PARTICLES Thisapplication is a continuation-in-part of our copending application, Ser.No. 590,959 filed Oct. 31, 1966 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates in general toimaging, and more specifically, to an improved migration imaging system.

There has been recently developed a migration imaging system capable ofproducing high quality images of high density, continuous tone and highresolution. This system is described and claimed in copendingapplications, Ser. Nos. 837,591 and 837,780 both filed June 30, 1969. Ina typical embodiment of this imaging system, a migration imagingstructure consisting of a conducting substrate with a layer ofsoftenable or soluble material containing migration material is coatedonto the conductive substrate. An electrostatic latent image is formedon the surface of the layer. The softenable layer is then developed bydipping the plate into a solvent which attacks only the soluble layer. Aportion of the migration material migrates through the softenable layeras it is softened or dissolved, leaving an image on the conductivesubstrate. Through the use of various materials, eitherpositive-topositive or positive-to-negative images may be made dependingon the materials used and the charging polarities. Those particles inthe softenable layer which do not migrate to the conductive substrateare washed away by the solvent with the softenable layer.

Three basic migration imaging structures exist: A layered configuration,which comprises a conductive substrate, a layer of softenable materialand an overcoating of migration material (usually particulate) embeddedin the upper surface of the softenable layer; a binder structure, inwhich the migration material is dispersed throughout the soluble layerwhich overcoats a conducting substrate; and finally an overcoatedstructure, in which a conductive substrate is overcoated with a layer ofsoftenable material followed by an overcoating of migration material anda second overcoating of softenable material which sandwiches themigration material. The migration imaging process consists of thecombination of steps which include charging, exposing and developmentwith a solvent liquid or vapor or a combination of vapor followed byliquid. If vapor development is used alone, the softenable layer may bestripped away leaving the migration image on the substrate. Thecharacteristics of these images are dependent on such process steps ascharging potential, light exposure and development as well as theparticular combination of process steps. High density, continuous toneand high resolution are some of the photographic characteristicspossible. The image is characterized as a fixed or unfixed powder imagewhich can be used in a number of applications such as microfilm, hardcopy, optical masks and stripout applications using adhesive materials.Alternative embodiments of these concepts are further described in theabove cited copending applications.

Another recently developed imaging system, utilizes nonphotoconductiveparticles contained in a non-photoconductive soluble layer on aconductive substrate. In this system, an electrostatic latent image isformed such as by corona charging through a mask or stencil. When theimaged sheet is exposed to a solvent for the softenable layer only, theparticles migrate to the substrate in image configuration. The unwantedparticles are washed away with the soluble layer. This system is alsodescribed and claimed in copending applications referred to above.

To prevent abrasion of the image formed by the migration imaging methodor loss of density, it is necessary to fix the image during developmentor by additional steps after development. In fixing during development,the developing liquid softens the conducting substrate or a thin film onthe substrate so that the image particles can become embedded in thesubstrate or thin film. In fixing after development, the developingliquid evaporates leaving a coating of dissolved plastic over the image.Thus, by using additional process steps after development, the image canbe fixed by either overcoating the image particles or by embedding themin the conducting substrate or in a thin film on the substrate. Astechniques require additions to the solvent developer or a specialcoating step, it can be seen that there is a definite need for a simpleand efficient image stabilizing step for migration images which avoidssoftening or overcoating the substrate, and yet produces images havinghigh resolution and excellent density.

It is, therefore, an object of this invention to provide a method ofstabilizing migration images which overcome the above noteddisadvantages.

It is another object of this invention to provide a simple and effectivemethod of stabilizing migration images.

It is yet another object of this invention to provide a method ofstabilizing selenium containing images.

It is a further object of this invention to provide an improvedmigration imaging process.

The foregoing objects and others are accomplished in accordance withthis invention by forming a migration image on a substrate followed byheating or chemically reacting the image forming material with theconductive substrate so as to produce a reaction between the substrateand imaging material, resulting in a permanent, stable image having highdensity and resolution. The advantages of this improved method willbecome apparent upon consideration of the following disclosure of theinvention; especially when taken in conjunction with the accompanyingdrawings wherein:

FIG. 1A is a schematic sectional view of a layered structure forcarrying out the invention.

FIG. 1B is a schematic sectional view of binder structure used incarrying out the invention.

FIG. 1C is a schematic sectional view of an overcoated structure forcarrying out the invention.

FIG. 2A is a schematic sectional view of the structure of FIG. 1A duringthe charging step.

FIG. 2B is a schematic sectional view of the structure of FIG. 1A duringthe exposure step.

FIG. 2C is a schematic sectional view of the structure of FIG. 1A duringthe development step.

FIG. 2D is a schematic sectional view of the structure of FIG. 1Afollowing development.

FIG. 2E is a schematic sectional view of the structure of FIG. 1A duringthe stabilizing step.

FIG. 1A shows a migration imaging plate comprising a conductivesubstrate 11 having thereon a softenable layer 12 overlaying theconductive substrate, and a layer 13 comprising migrationmaterialusually in particulate form.

The substrate 11 upon which the softenable plastic and particulatemigration material are formed may be any suitable conductive substratewhich will react chemically with the migration material. Typicalsubstrates are copper, chromium, brass, cadmium, silver and gold. Thesubstrate may be in any form such as a metallic sheet, web, foil,cylinder or the like. If desired, the conductive metal may be coatedover an insulator such as paper, glass or plastic.

The softenable plastic layer 12 may be any suitable material which issoftened in a liquid or vapor solvent; and in addition, is substantiallyelectrically inert during the imaging and developing cycle. Typicalmaterials are Staybelite Ester 10, a partially hydrogenated rosin ester,Foral Ester, a hydrogenated rosin triester and Neolyne 23, an alkydresin, all from Hercules Powder Co.; SR 82, SR 84, silicone resins, bothobtained from General Electric Corporation; Sucrose Benzoate, EastmanChemical; Velsicol X-37, Hydrogenated Velsicol X-37, Velsicol ChemicalCorp., Hydrogenated Piccopale 100, a highly branched polyolefin,Piccotex 100, polystyrene-vinyl toluene, Piccolastic A-75, and 125, allpolystyrenes, Piccodine 2215, a polystyrene-olefin copolymer, all fromPennsylvania Industrial Chemical Co.; Araldite 6060 and 6071, epoxyresins of Ciba; R5061A, a phenyl-methyl silicone resin from Dow Corning;Epon 1001, a bisphenol A- epichlorohydrin epoxy resin, from ShellChemical Corp., and

PS-2, PS-3, both polystyrenes and ET-693, a phenol-formaldehyde resin,from Dow Chemical. Other materials useful as the softenable layer aredescribed in copending application, Ser. No. 837,780 filed June 30,I969, which is incorporated herein by reference.

The above group of materials is not intended to be limiting, but merelyillustrative of materials suitable for the softenable plastic layer. Thesoftenable plastic layer may be of any suitable thickness. In general,the thicker the layer the greater the potential needed for charging. Athickness from about 1 to 4 microns has been found satisfactory, butlayers outside this range will also work.

The material 13, which constitutes the migration material, may be anysuitable migratable material which reacts with the metal selected forthe substrate. Typical migration materials are photoconductors such asparticulate vitreous selenium, and alloys of selenium such as telluriumand selenium, cadmium sulfide, cadmium sulfoselenide and arsenictriselenide. Other migration material, photoconductive ornon-photoconductive, is described in the above mentioned copendingapplication, Ser. No. 837,780. Of course, the migration material isselected on the basis of its reactivity with the metal employed at thesubstrate. The size of the migration particles range from about 0.01 to1.5 microns in diameter and may be prepared by vacuum evaporationtechniques such as those disclosed in copending application, Ser. No.423,167, filed on Jan. 4, 1965, and now abandoned. Another convenientmethod of forming the particulate migration layer is by simply dustingor cascading the material on glass carrier beads over the soluble layersoftened by solvent vapor. This method is disclosed in copendingapplication, Ser. No. 483,675, filed on Aug. 30, 1965. The thickness ofthe migration layer is from about 0.2 to

14 microns with the thicker layers being in the binder form.

In FIG. 1B, the binder form of the structure is shown in which themigration particles 13 are dispersed throughout soluble layer 12.

The structure of FIG. 1C shows the overcoated structure in which themigration particles 13 are sandwiched between two layers of solublematrix material 12 which overlays conductive substrate 11. Both thebinder and overcoated structure shown in FIGS. 13 and 1C, respectivelycontain essentially the same basic materials as illustrated for thelayered structure shown in FIG. 1A.

In FIG. 2A the layered structure of FIG. 1A is uniformly charged overits entire surface by a corona discharge device 14, such as that shownin US. Pat. No. 2,777,957 to Walkup. The potential required formigration imaging has been shown to depend on a number of factors. Forexample, the form of the imaging structure such as the three illustratedin FIGS. 1A, 1B and 1C, the thickness and material used in the solublelayer, the type of migration material used, the developing solvent, thecombination of process steps, the polarity of the potential and thelight exposure, etc. If the potential is too high, the migrationparticles are usually deposited on the conducting substrate randomlywithout regard to light exposure. If, on the other hand, the potentialis too low, none of the particles are deposited. In general, thepotential may range from a few volts to 400 volts with a soluble layerof about 2 microns in thickness depending upon the material used.Generally, it may be said that the potential increases with thethickness of the soluble matrix layer for a given matrix material. For afew combinations of material, images can be obtained with potentials foronly one polarity. For some combinations of migration materials andsoluble layers, the maximum potential is higher for positive than fornegative polarity. For example, this was observed with selenium vacuumevaporated on several different matrix materials.

Other methods of forming an electrostatic image on the surface of thephotoconductive layer are also included within the scope of thisinvention. Such methods include corona charging through a stencil asshown in copending application, Ser. No. 483,675, filed on Aug. 30,1965. In addition, the migration imaging structure may be chargedthrough a liquid by an electrode using a low viscous liquid such as asilicone oil.

In FIG. 2B the imaging or exposure step takes place with exposing light15 selectively impinging upon the charged surface containing, forexample, photoconductive particles 13. The exposure for migration imagesdepends upon the photoconductor, potential and its polarity, thecombination of the process steps in the form of the imaging structureand the material of the soluble layer and solvent used in development.

. As in xerographic imaging, any amount of light suitable to activatephotoconductor material 13, is usually sufficient to form an image. Forexample, the minimum exposure for maximum density with 4,000 angstromlight is approximately 1.5 x 10 photons/cm. with a structure consistingof selenium vacuum evaporated on Staybelite, 2 microns thick. This sameexposure discharges a 50 micron conventional xerographic selenium platefrom 600 volts to 500 volts.

In FIG. 2C the development step for the migration imaging structure isillustrated, wherein the structure is developed by immersing in asolvent for soluble layer 12. The solvent liquid 16 may be applied tothe structure by spraying, pouring or dipping the structure into theliquid. The development time is not particularly critical inasmuch asthe solvent is selected so as to dissolve only the softenable or solublelayer and be relatively neutral with regard to the photoconductiveparticles and conducting substrate. The development time is dividedessentially into two parts; the time for imagewise migration of theparticles to the conducting substrate and thetime for flushing away theunmigrated particles. The development time ranges from less than 1second with a layered structure 3 microns thick, such as thatillustrated in FIG. 1A, to about 45 seconds using a binder structuresuch as that illustrated in FIG. 1B having a binder structure about 12microns thick. The flushing time, and hence the developing time, can bereduced by increasing the relative motion between the solvent andimaging structure.

The solvent developer liquid 16 may comprise any suitable solvent forthe soluble layer 12. Typical solvents are Freon TMC (duPont);trichloroethylene, chloroform, ethyl ether, xylene, dioxane, benzene,toluene, cyclohexane, 1,1 ,ltrichloroethane, pentane, n-heptane,Odorless Solvent 3440 (Sohio); Freon 1 l3 (duPont), m-xylene, carbontetrachloride thiophene, diphenyl ether, p-cymene, cis-2,2-dichloroethylene, nitromethane, ethanol, ethyl acetate, methyl ethylketone, ethylene dichloride, methylene chloride, 1,1-dichloroethylene,trans 1,2-dichloroethylene and super naptholite, (Buffalo Solvents andChemicals). Other developer liquids are described in copendingapplication, Ser. No. 837,780.

After developing in the solvent liquid as shown in FIG. 2C, thephotoconductor 13 is formed in image configuration on substrate 1 l asshown in FIG. 2D. At this point in order to stabilize image 13, and atthe same time increase the density of the image, a stabilizing stepwhich comprises reacting image 13 with substrate 11 is carried out asshown in FIG. 2E. The stabilizing step involves heating the imagebearing substrate 11 with any suitable heating means such as aconducting coil 19 in order to react the substrate 11 with thephotoconductor material and cause a chemical reaction between saidphotoconductive material and the substrate. Other heating means such ashot air, gas burners, etc., may of course, be used. During the heatingstep, the photoconductor material in the image area agglomerates usuallyproducing an initial reduction in density due to fading, but after thereaction with the substrate, the photoconductive material appears to wetand spread over the substrate resulting in a stable image having highdensity and illustrated by 13 As already mentioned above, the substratemay take any form or configuration as long as the reactive metal is atthe exposed surface to receive the migration material after development.

For the purpose of illustrating the invention, a conventional migrationimaging member containing a copper substrate, and having a 2-micronlayer of Staybelite Ester 10, a 50 percent hydrogenated glycerol rosinester of the Hercules Powder Company, overlaying the copper substrate,with a 0.2-micron layer of vapor deposited selenium deposited in theupper surface of the Staybelite is treated as follows:

The plate is first charged by a corona charging device to a positivepotential of about 100 volts (FIG. 2A). The plate is tial of about 60volts by means of a corona discharge device described by Carlson in U.S.Pat. No. 2,588,699. The charged plate is then exposed to an opticalimage with an energy in the illuminated areas of about 10foot-candle-seconds by means of then exposed to an optical image ofabout 10 foot-ca dl 5 a tungsten chamber and a weak blue filter. Theplate is then seconds in the illuminated areas using a tungsten lamp(FIG. developed y immersing it in a bath of eyeloheireme for about 28).Development of the plate is carried out by immersion in 2 secolids' ThePlate is removed from the developer bath arid Freon 113, a halogenatedhydrocarbon available from the E. I. drled- An excellent imagecorresponding to the Projected duPont de Nemours Co., Inc. for about 2seconds and then 10 image is observed outhe P t This image cempnses athin removed and dried in air (FIGS 2 and 2 The particulate layer ofselenium particles in image configuration on a copper image is thenstabilized by heating the substrate to a tempera- Substrate EXAMPLE tureof about 100 C. for about 1 minute to react the copper substrate withthe selenium particulate image. This reaction The plate of Example I isthen placed in a sealed glass yields a black crystalline material havinga melting point of chamber and exposed to vapors of mercury for about 5about LOOOO minutes. At the end of this time, the plate is removed fromthe During the heating, the selenium in the image ea glass chamber andheated by hot air to a temperature of about glomerates r d i an i i i lreduction i d i f di 100 C. for several minutes, at which time theselenium and but after the reaction, the selenium appears to wet andspread the substrate react, with the Selenium appearing to wet arid overthe copper substrate. The fading can be prevented by spread Over the ppSubstrate The resultant image shows first converting the surface ofselenium in the image areas to a high density, excellent contrast and isresistant l0 abrasion and crystalline form, followed by heating toproduce the chemical thoroughly Stable at relatively hightemperaturesreaction at the copper-selenium surface. Thiscrystallization can be produced by exposure of the image to any knownele- EXAMPLE In ment or compound which will crystallize the surface ofthe A i i plate using h copper t d M l Substrate selenium or seleniumalloy in the image areas. These agents inas i E l I i lh d i h a 2- ilayer f pi elude Vapor treatments with mercury, iodine, Chlorine, 100,(Pennsylvania Industrial Chemical Company). This plate bromine fluorine,amines Such as hexyiamine, For Examis coated with a selenium layer anddeveloped in cyclohexane ple, exposure to mercury vapors for about 5minutes is usu y as in Example I. The plate is then exposed anddeveloped as in Sufficient to Convert the surface to a Crystalline rorm-Example II and shows a stable image following mercury vapor The reactiontemperature is that temperature at which the treatment and heatstabilization as set forth in Example II. selenium will react with thegiven substrate. This temperature is only critical with respect to thesubstrate in that it should EXAMPLES IV'IX not exceed a temperaturewhich will p buckle the The procedures set forth in Examples I and IIare carried Strate' out with a series of plates which are prepared,imaged, Generally, temperatures in the range of about 90 to 350 C.developed and stabilized under varying conditions with the aresufficient to react the selenium or selenium containing results andprocess parameters set forth in the table below for alloy with thesubstrate. 40 all of the samples prepared and tested in the examples.

TABLE Heat Softenahle Photoconductive Mercury stabili- Sample ConductivePlastic (2 Layer (1 micron Developer (1-3 vapor trcatzation, No.Substrate microns thick) thick) Potential Exposure seconds in bath)ment, min. C

I Copper Staybelite Selenium 100 4,000 Angstrom light Z... Freon 113 5100 2.. do. Picc0tex d +100 do. o 5 100 3.. Copper foil Staybelite +100do. Carbon tetrachlo 5 100 4 +100 (10. 1% 5 I00 5 Cyclohexane... 5 100 6-d0 do 5 100 7 Cadmium sulfide. .do 320 8... Polyvinyl carbazole- 270 9Copper do Cadmium sul- 320 ioselenlde.

1 (0.1 micron) on 3 mil Mylar.

3 5 mil.

' (300 angstroms) on Glass Slide.

EXAMPLEI An imaging plate such as that illustrated in FIG. 1A isprepared by roll-coating a Z-micron layer of Staybelite Ester l0(Hercules Powder Company) on a 3-mil Mylar polyester film (E. I. duPontde Nemours & Co., Inc.) having a thin coating of copper about 0.1 micronthick. A thin layer of vitreous selenium approximately 1 micron inthickness, is then deposited onto the Staybelite by inert gas depositionusing the process set forth in copending patent application, Ser. No.423,167, filed on Jan. 4, 1965. The plate is then electrostaticallycharged under dark room conditions to a positive poten- What I claim is:

1. A method for stabilizing a migration image comprising a. providing amigration imaging member having a conductive substrate comprising ametallic layer and an electrically insulating solvent soluble over-layercontaining migration material, said migration material comprisingselenium particles b. forming an electrostatic latent image on saidmember;

c. developing said image by applying a solvent for said electricallyinsulating layer to said member wherein a portion of the seleniumparticles deposit in image configuration on said conductive substrateand wherein another portion of selenium particles and said electricallyinsulating layer are removed from said substrate; and

d. heating said substrate and said selenium particles residing thereonto a temperature not exceeding the temperature which will warp or bucklesaid substrate whereby a chemical reaction occurs between said metalliclayer and said selenium particles.

2. The method as defined in claim 1 wherein said electrostatic latentimage is formed by uniformly charging said migration imaging member andselectively illuminating said charged member with a pattern ofactivating radiation.

3. The method of claim 1 wherein the conductive substrate comprisescopper.

4. The method of claim 1 wherein the conductive substrate comprisesbrass.

5. The method of claim 1 wherein the conductive substrate comprisescadmium.

6. The method of claim 1 wherein the conductive substrate comprisessilver.

7. The method of claim 1 wherein the conductive substrate comprisesgold.

8. The method of claim 1 wherein the migration material comprisesvitreous selenium.

9. The method of claim 1 wherein the migration material comprises avitreous alloy containing at least 50 percent selenium by weight.

10. The method of claim 8 wherein the developed image of claim 1 istreated with a crystallizing agent prior to step (d).

l 1. The method of claim 10 wherein the crystallizing agent comprisesvapors of mercury.

12. The method of claim 1 wherein the conductive substrate compriseschromium.

2. The method as defined in claim 1 wherein said electrostatic latentimage is formed by uniformly charging said migration imaging member andselectively illuminating said charged member with a pattern ofactivating radiation.
 3. The method of claim 1 wherein the conductivesubstrate comprises copper.
 4. The method of claim 1 wherein theconductive substrate comprises brass.
 5. The method of claim 1 whereinthe conductive substrate comprises cadmium.
 6. The method of claim 1wherein the conductive substrate comprises silver.
 7. The method ofclaim 1 wherein the conductive substrate comprises gold.
 8. The methodof claim 1 wherein the migration material comprises vitreous selenium.9. The method of claim 1 wherein the migration material comprises avitreous alloy containing at least 50 percent selenium by weight. 10.The method of claim 8 wherein the developed image of claim 1 is treatedwith a crystallizing agent prior to step (d).
 11. The method of claim 10wherein the crystallizing agent comprises vapors of mercury.
 12. Themethod of claim 1 wherein the conductive substrate comprises chromium.